Orthosis knee joint

ABSTRACT

A selectively lockable orthotic joint is provided that in one embodiment includes at least one pressure sensor and an electronic circuit associated with the pressure sensor for generating or providing a control signal indicative of pressure, force or other value sensed by the sensor. A mechanical orthotic joint is provided that has a locking mechanism that can be selectively locked and unlocked in response to the control signal.

This application claims the benefit of prior filed co-pending U.S.Provisional Application Serial No. 60/101,084, filed Sep. 18, 1998, thedisclosure of which is hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to orthoses for providing assistance inwalking. More particularly, the present invention relates to an improvedknee joint for such an orthosis.

An orthosis is a brace or other orthopedic device that is applied to asegment of a human body for the purpose of assisting in the restorationor improvement of its function. Orthoses can provide assistance inwalking to persons having any of several types of walking disability.One known type of orthosis is a knee/ankle/foot orthosis which controlsthe motion and alignment of a knee and an ankle when a person attemptsto walk. Such orthoses can be made of molded plastic materials or ofmetal and leather parts, Various knee and ankle joints can be added toachieve the desired function.

Typical reasons for wearing such an orthosis include stroke, braininjuries, spinal cord injury and post-polio treatment. A person who isnot able to move his leg in a functional manner to ambulate, must wear aknee/ankle/foot orthosis to stabilize his leg and allow for ambulation.It has been found that for people with weak knee joints, a lockingmechanism is necessary in order to lock a calf supporting orthosis toprevent movement in relation to a thigh supporting orthosis, therebyallowing the person to walk, albeit stiff legged.

There are many types of knee joints used on such orthoses. However, allthe known joints which lock during ambulation are manual. In otherwords, when a patient is using the orthosis, he has a choice of walkingwith his leg locked in extension or in a free swing. If the patientchooses the locked position, he is forced to walk stiff legged. However,for some people, flexing at the knee during walking would result in abuckling of the person's leg. Therefore, walking stiff legged is muchpreferable to being not able to walk at all. Of course, a movement ofthe calf orthosis in relation to the thigh orthosis is necessary whenthe person decides to sit down.

As far as is known, there are no knee joints currently on the marketwhich have the ability to automatically lock and unlock without directmanual patient intervention.

Accordingly, it has been considered desirable to develop a new andimproved orthosis knee joint which would overcome the foregoingdifficulties and others while providing better and more advantageousoverall results.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an orthosisfor assistance in walking.

More particularly in accordance with this aspect of the invention, theorthosis includes an orthosis system which comprises a foot plateincluding at least one pressure sensor that senses the pressure exertedby a patient's foot on the foot plate, a circuit connected to at leastone pressure sensor in the foot plate and a knee joint which isselectively locked and unlocked by the circuit. To this end, the kneejoint is electrically operated.

In accordance with the present invention, a selectively lockableorthotic joint is provided. The selectively lockable orthotic jointincludes at least one pressure sensor which can be used to sense aperson's weight or a portion thereof, and may be a sensor to beassociated with a person's foot, for example. An electronic circuit isprovided that is associated with the pressure sensor for generating acontrol signal indicative of pressure or weight sensed by the sensor. Atleast one mechanical orthotic joint that incorporates a lockingmechanism is included which orthotic joint can be selectively locked andunlocked in response to the control signal.

More particularly, the mechanical orthotic joint of the selectivelylockable orthotic joint invention includes an energizableelectromagnetic coil, a spring washer deflectable in an axial directionwhen the electromagnetic coil is energized and an arrangement of firstand second plates. The first plate has a face or an operative surfacecomposed of a plurality of spaced teeth. The second plate also has aface or an operative surface having a plurality of spaced teeth that arecomplementary to the plurality of spaced teeth of the first plate. Thesecond plate is mounted so that it is deflectable in an axial directionsuch that the plurality of spaced teeth of the second plate can engagethe plurality of spaced teeth of the first plate when theelectromagnetic coil is energized. The engagement of the first andsecond plates locks movement of the orthotic joint in at least onedirection when the first and second plates are engaged.

In accordance with one embodiment, the first and second plates arecomplementary and each comprise ratchet plates allowing the orthoticjoint to move only in one direction when the joint is in a lockedposition. More specifically, in one embodiment, when unlocked theorthotic joint is movable in a flexion direction and an extensiondirection and when the orthotic joint is locked, it is movable only inthe extension direction.

The first and second plates may comprise a low hysteresis magneticmaterial.

In accordance with another aspect of the present invention, a method forselectively locking and unlocking an orthotic joint is provided. Oneembodiment locks the orthotic joint to permit movement only in theextension direction.

In accordance with the method, an orthotic joint of the type previouslydescribed is utilized. Pressure is sensed by the pressure sensor and anelectronic control signal is generated with the electronic circuit thatis indicative of pressure sensed by the pressure sensor. In response tothe electronic control signal, the orthotic joint locks through itslocking mechanism.

One advantage of the present invention is the provision of a knee jointwhich allows patients, who are currently walking stiff legged with alocked knee joint in a knee/ankle/foot orthosis, to walk with a morenormal gait.

Another advantage of the present invention is the provision of anorthosis which will make sitting and standing much safer and easier forany patient forced to manually unlock his knee joint.

Still another advantage of the present invention is the provision of anorthosis system which senses the pressure placed by a patient's foot ona foot plate of the orthosis and can automatically trigger a knee jointof the orthosis to lock and unlock. The knee joint will be locked whenpressure is placed by the patient's foot on the foot plate. It will beunlocked when the patient's foot no longer exerts pressure on the footplate.

In accordance with another aspect of the invention, a selectivelylockable orthotic joint is provided. The selectively lockable orthoticjoint includes an electronic circuit for providing at least one controlsignal indicative of a value. At least one mechanical orthotic joint isprovided that includes a locking mechanism that is in communication withthe circuit. The locking mechanism can be selectively locked andunlocked in response to the control signal. The control signal providedby the electronic circuit can originate from a variety of sources otherthan by sensing pressure or weight. For example, the control signal canoriginate from EMG signals in leg muscles, from EEG signals, from asensor that detects distance between the ground and the bottom of a shoeor other article, such as a cane, for example. In addition, a controllercould be provided for operation by the user, such as a joy stick orother type of switch in order to generate or otherwise provide thecontrol signal for locking and/or unlocking the locking mechanism of themechanical orthotic joint.

Still other benefits and advantages of the invention will becomeapparent to those of average skill in the art upon a reading andunderstanding of the following detailed specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, a preferred embodiment of which will be described in detail inthis specification and illustrated in the accompanying drawings whichform a part hereof and wherein:

FIG. 1A is a side elevational view in cross section along line 1A—1A ofFIG. 13 of a knee joint according to the present invention in anunlocked condition;

FIG. 1B is a side elevational view in cross section of the knee joint ofFIG. 1A in a locked condition;

FIG. 2A is a top plan view of the toroidally shaped housing of the jointof FIG. 1A;

FIG. 2B is a cross-sectional view taken along line 2B—2B of FIG. 2A;

FIG. 3A is a top plan view of a bottom ratchet plate of the knee jointof FIG. 1A;

FIG. 3B is a side elevational view in cross section along line 3B—3B ofFIG. 3A;

FIG. 4A is a bottom plan view of a top ratchet plate of the knee jointof FIG. 1A;

FIG. 4B is a side elevational view in cross section along line 4B—4B ofFIG. 4A;

FIG. 5A is a top plan view of the top end portion of the knee joint ofFIG. 1A;

FIG. 5B is a side elevational view in cross section taken along line5B—5B of FIG. 5A;

FIG. 6 is a top plan view of an inner retaining ring of the knee jointof FIG. 1A;

FIG. 6A is a cross-sectional view along lines 6A—6A of FIG. 6;

FIG. 7 is a top plan view of the retaining cap of the knee joint of FIG.1A;

FIG. 7A is a cross-sectional view along line 7A—7A of FIG. 7;

FIG. 8 is a top plan view of an outer retaining ring of the joint ofFIG. 1A;

FIG. 9 is a top plan view of a spring washer of the joint of FIG. 1A;

FIG. 10 is an exploded perspective view of components of the knee jointof FIG. 1A;

FIG. 11 is a circuit diagram of a circuit which is employed with theknee joint of FIG. 1A and the force or pressure sensor of FIG. 12;

FIG. 12 is a perspective view of the force or pressure sensor employedwith the joint of FIG. 1A;

FIG. 13 is a perspective view of an orthosis in accordance with theinvention incorporating the joint of FIG. 1A and the sensor of FIG. 12;

FIG. 14 is a fragmentary perspective exploded view of an alternateembodiment joint in accordance with the invention; and

FIG. 15 illustrates a cross-sectional schematic view of a portion of thealternate embodiment of FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the drawings are for purposes ofillustrating a preferred embodiment of the invention only and not forpurposes of limiting same, FIGS. 1A and 1B, 10 and 13, for example, showa knee joint 10 which is used in an orthosis 10′ or orthopedicappliance, for example in FIG. 13. It is evident that two such kneejoints would need to be employed for the two legs of a patient, onejoint for each leg of the patient. Perhaps, even four knee joints couldbe used, one on either side of the knee of each leg of the patient. Itis to be understood that joint 10 could be used other than as a kneejoint, for example.

Joint 10 includes a toroidally shaped housing 12. Toroidally shapedhousing 12 is depicted individually in FIGS. 2A and 2B. With referencenow to FIGS. 2A and 2B, the toroidally shaped housing 12 has an innerwall 14, a base wall 16 and an outer wall 18 which together define acavity 20. A plurality of spaced teeth 22 protrude upwardly from theinner wall 14. Preferably, eight such teeth are provided, although anysuitable number of teeth can be utilized. A continuous flange 24 extendsupwardly from the outer wall 18. A rib 26 extends radially inwardly fromthe inner wall 14 into a central opening 28 to form a toroidal ledge 26′approximately half way up the height of the inner wall.

With reference again to FIGS. 1A and 1B and 10, an electromagnetic coil30 is located in cavity 20. Electromagnetic coil 30 is formed around aplastic bobbin 32. Positioned on either side of rib 26 are a firstbearing 34 and a second bearing 36. The bearings can be conventionalroller bearings or other suitable bearings, as desired. A bottom ratchetplate 38 is also provided for the knee joint. Bottom ratchet plate 38 isdepicted in greater detail in FIGS. 3A and 3B. Bottom ratchet plate 38includes a planar bottom surface 40, as illustrated in FIG. 3B, and atop face 42 having a plurality of radially extending spaced teeth 44protruding therefrom. As is evident from FIG. 3A, sixty such teeth 44are preferably located on the top face 42 with each tooth being spacedfrom the adjacent teeth by slots, although any suitable number of teethcan be utilized. Preferably, the teeth 44 are cut in a saw tooth patternradially at a 30 degree slope. A set of eight spaced slots 46 are cutinto the bottom ratchet plate 38. The slots extend radially outwardlyfrom a central opening 48 of the plate 38 as is evident from FIG. 3A.

The joint of FIGS. 1A and 1B is further provided with a top ratchetplate 50, which is shown in more detail in FIGS. 4A and 4B. Top ratchetplate 50 is preferably constructed of a magnetically soft material, forexample a low hysteresis, solenoid quality magnetic stainless steel.Bottom plate 38 may be constructed of similar material. With referencenow to FIG. 4A, top ratchet plate 50 includes a top face 52 (FIG. 4B)and a bottom face 54. A plurality of spaced teeth 56 are cut into thebottom face 54. Preferably sixty such teeth are provided. As with thebottom plate 38, the teeth 56 in the top plate are cut in a saw toothpattern radially at a 30 degree slope such that a tip of each tooth isseparated from a tip of each adjacent tooth by 6 degrees. The teeth 56of the top ratchet plate are meant to be and should be of suitabledesign and number to engage and mesh with the teeth 44 of bottom ratchetplate 38 when the two ratchet plates are brought into contact with eachother. Also provided on top ratchet plate 50 is a slot 58 whichcircumscribes the teeth 56. A plurality of spaced apertures 60′ extendthrough top ratchet plate 50. These apertures are positioned radiallyoutwardly of slot 58. As is evident from FIGS. 1B and 10, suitablefasteners 60 can extend into the top ratchet plate apertures.

With reference now to FIGS. 1A, 1B and 10, a shaft 62 is also provided.As shown in FIGS. 5A and 5B shaft 62 includes a stem portion 64 and anenlarged top end 66 having a set of spaced apertures 68 extendingtherethrough. Note that in FIGS. 5A and 5B, the diameter of flange 66 isillustrated smaller than the diameter illustrated in the other figures.A bottom end of the stem portion 64 is provided with a centrally locatedaperture 70. Each of these apertures accommodates suitable fasteners 60and 61. Referring to FIGS. 1A and 1B, also provided is an innerretaining ring 72. As detailed in FIG. 6, inner retaining ring 72 has acentral aperture 72′ for accommodating stem portion 64 and includes aset of apertures 74 extending therein. Each of apertures 74 is alsomeant to accommodate a suitable fastener 60. A retaining cap 76 is alsoprovided. As shown in FIGS. 7 and 7A, retaining cap 76 has a centrallyextending aperture 78 for accommodating a suitable fastener 61.Fasteners 60 and 61 can be threaded fasteners or any other suitable typeof fastener, for example.

Joint 10 is also provided with an outer retaining ring 80. As shown inFIG. 8 a set of apertures 82 extend through retaining ring 80 toaccommodate suitable fasteners 60. As shown in FIGS. 1A, 1B, 9 and 10, aspring washer 84 is further provided. Spring washer 84 is preferablycomprised of a plurality of very thin pieces of metal which, whenassembled, is very compliant in an axial direction while maintaining ahigh rigidity in torsion. For example, spring washer 84 may consist ofapproximately 60 pieces of 0.001 inch thick stainless steel disks. Theaxial compliance allows the spring washer to be deflected at relativelylow electromagnetic forces allowing the upper ratchet plate to mesh withthe lower ratchet plate. Spring washer 84, further depicted in FIG. 9,has a set of outer apertures 86 for accommodating a suitable first setof fasteners 60 and a set of inner apertures 88 similarly foraccommodating a suitable second set of fasteners 60. Spring washer 84also has a central opening 90 to accommodate stem portion 64 of shaft62.

Spring washer 84 is very compliant in the axial direction, permittingdeflection of upper ratchet plate 50 even with relatively lowelectromagnetic attraction forces, typically deflecting about {fraction(1/16)}^(th) of an inch in an axial direction with an electromagneticforce of several pounds. Thus, the significant axial deflection that isobtained with low electromagnetic forces permits operation of joint 10at low power consumption levels which is important for battery-operateduse. Spring washer 84, however, is strong and stiff in torsion,providing the necessary reaction torque to support the moments requiredin an orthotic application. Any suitable washer that performs thefunction of spring washer 84 can be utilized in accordance with theinvention.

As is evident from FIGS. 1A, 1B and 10, shaft 62 is located in centralopening 28 of toroidally shaped housing 12. Retaining cap 76 is fastenedto shaft 62 by fastener 61. In this way, two bearings 34 and 36 can besecured in place in central opening 28 of housing 12. Bottom ratchetplate 38 is seated on inner wall 14 of housing 12. To this end, severalspaced slots 46 in bottom ratchet plate 38 accommodate several spacedteeth 22 in housing 12. More particularly, eight slots 46 and eightteeth 22 are provided in housing 12. It is apparent that no keying isnecessary since bottom ratchet plate 38 can be rotated in relation tothe housing to any desired extent so long as the slots 46 are alignedwith teeth 22.

Top ratchet plate 50 is positioned above bottom ratchet plate 38. In thecondition illustrated in FIG. 1A, top ratchet plate 50 is spaced frombottom ratchet plate 38. This allows a movement of joint 10 in eitherrotational direction (flexion or extension). In the position illustratedin FIG. 1B, the teeth of top ratchet plate 50 engage the teeth of bottomratchet plate 38 to prevent any further rotation of the joint.Preferably, the two ratchet plates are spaced from each other asindicated when in the unactuated state as shown in FIG. 1A.

With reference again to FIG. 1A, spring washer 84 is fastened to flange66 of shaft 62 via inner retaining ring 72. Spring washer 84 is alsofastened to top ratchet plate 50 and outer retaining ring 80 byfasteners 60. In this way, top ratchet plate 50 is normallyspring-biased away from bottom ratchet plate 38. However, top ratchetplate 50 is pulled into contact with bottom ratchet plate 38 whenelectromagnetic current is flowing through electromagnetic coil 30.

With reference now to FIG. 11, a circuit 100 which includes anintegrated circuit 100′, which can be a Microchip Model No. PIC16C715,is employed to control the operation of joint 10. The integrated circuitis preferably powered by a pair of 3 volt batteries 102 and 104.Electromagnetic coil 30 is preferably powered by a pair of 1.5 voltbatteries 106 and 108.

With reference now to FIG. 12, an insole pressure or foot force sensor110 is also used in connection with the joint 10. More particularly, aset of output lines 112 lead from a set of sensors 114 in the insole tocircuit 100. Batteries 102 and 104 provide a reference signal for thesensors. A pair of output lines 116′ from circuit 100 extend to theelectromagnetic coil 30. The pair of 1.5 volt batteries 106 and 108,which are of relatively higher power than the power of the 3 voltbatteries, are meant to power the electromagnetic coil.

Insole pressure sensor 110 is preferably provided with five sensorswhich detect pressure by a voltage drop across very thin resistors, forexample the foot force sensor provided by Cleveland Medical Devices,Inc. It should be apparent to one skilled in the art that more or lesssensors may be used. The insole is slipped inside a patient's shoe. Thesignal from the insole is translated through wires 112 to circuit 100.Integrated circuit 100′ also contains a programmable microprocessor. Anysuitable microprocessor can be utilized. The processor determines athreshold level and sends a signal to the joint 10 attached to a kneejoint as depicted in FIG. 13. However, the joint need not be limited toa knee joint, but may also be an ankle, wrist or elbow joint. Anysuitable pressure or force sensor can be used in accordance with theinvention.

With the orthosis of the present invention, when a person puts his footon the floor, the sensors 114 in insole sensor 110 sense a pressure andcan trigger the joint 10 to lock by energizing electromagnetic coil 30thereby bringing the top ratchet plate 50 down into contact with bottomratchet plate 38 engaging respective teeth 56 and 44. Preferably, thisaction prevents any further rotation of the joint in one rotationaldirection, however, this may lock the joint entirely from rotating. Moreparticularly, top ratchet plate 50 and shaft 62 cannot rotate viabearings 34 and 36 in relation to bottom ratchet plate 38 and housing 12toward a bent knee position. Preferably, when the teeth of the upper andlower ratchet plates are engaged, the joint allows incremental slip(ratcheting) in a joint extension. However, when no more pressure issensed by sensors 114 of the insole sensor 110, circuit 100 will unlockthe knee joint by ceasing the flow of electric current in theelectromagnetic coil.

Once this occurs, spring washer 84 will pull top ratchet plate 50 out ofengagement with bottom ratchet plate 38. This will allow a rotation ofthe knee joint in both directions. In particular, top ratchet plate 50and shaft 62 are again capable of rotating in relation to bottom ratchetplate 38 and housing 12. Thus, the joint is unlocked when pressure ofthe patient's foot is no longer exerted on the insole sensor 110. Thisinvention will allow a user who is currently wearing stiff leggedknee/ankle/foot orthoses to walk with a more normal gait. In addition,it will make sitting and standing safer and easier for any usercurrently forced to manually unlock their knee joint.

When a threshold level is reached, a magnetic field is generated byelectromagnetic coil 30 to pull top ratchet plate 50 into engagementwith bottom ratchet plate 38, no longer allowing the two ratchet platesto rotate freely in relation to each other. This locks the knee jointand prevents it from bending into flexion. However, the joint will stillallow extension. As an example, if the patient is attempting to standand gets stuck halfway up, the joint will block flexion and prevent thepatient's knee from buckling. But, it will still ratchet into extensionand allow the patient to continue moving vertically. Thus, a veryimportant advantage of the present invention is the provision of a kneejoint in which flexion is prevented when the top ratchet plate 50 mesheswith bottom ratchet plate 38 but extension is still allowed. This isaccomplished due to the orientation of the meshing teeth 44 and 56 ofthe bottom and top ratchet plates 38 and 50.

As a second example, a user, when he takes a step, will have the insoleread the floor contact and lock the knee for the user. The knee remainslocked through the step and then unlocks when the user initiates swingthrough, i.e. takes the pressure off the first leg and puts the pressureon the second leg. The knee joint will then lock again at the nextinitial floor contact.

Sensors 114 could be wired in series or in parallel for the signal whichis sent through wires 112 to circuit 100. Preferably, the output of allof sensors 114 is summed together. If a set point is reached,electromagnetic coil 30 is triggered and the knee joint is locked.However, the logic of the chip on the integrated circuit could beprogrammed to differentiate between, e.g. a heel strike and a toe strikeof the foot plate. The logic of the circuit may also provide that givenpatterns of pressure, for example placing pressure on only inner orouter pressure sensors, detected by the sensors could disengage theteeth in the joint permitting an individual to sit.

Joint 10 according to the present invention can be attached to anyconventional knee/ankle/foot/elbow/wrist orthosis or any knee brace aslong as the brace is fabricated to the joint size specification. Aperson skilled in the art should realize that the orthotic joint of thepresent invention supports passive locking arrangements wherein thejoint is locked until the coil is magnetized which unlocks the joint asopposed to the active locking embodiment of the joint as describedabove.

FIGS. 14 and 15 illustrate an alternate embodiment of an electronicallycontrolled orthotic joint according to the present invention. Thisembodiment as shown in FIGS. 14 and 15 provides an electromagnetic coil118 located within a housing 120. Actuating portion 122 is provided aswell as opposing teeth inserts 124 and 126. Engagement of the teethinserts 124 and 126 is actuated by energizing coil 118. The coil isenergized under control of a microprocessor (not shown) as in the aboveembodiment. Energizing the coil produces an axial force on actuatingportion 122 which forces teeth insert 124 into engagement with teethinsert 126. In this embodiment, a passive spring (not shown) causes theteeth of teeth inserts 124 and 126 to disengage upon interruption ofcurrent through coil 118. This embodiment can also provide forincremental slip in a single rotational direction as desired. Further,teeth inserts 124 and 126 are constructed of non-magnetic material sothat they may be made of a more durable material, for example toolsteel. This embodiment also provides a spline interface (not shown)between outer support ring 130 and actuating element 122. This splineinterface is on the internal surface of outer support ring 130 and theexternal surface of actuating element 122. This spline interface permitsaxial translation of actuating element 122 while enabling large torquesto be transmitted from outer support ring 130 to actuating element 122.This arrangement permits application of large torques from outer supportring 130 to the opposite outer support ring 128 as follows. Torques aretransmitted from element 130 to element 122 via the spline interface.Torques are thus transmitted from actuator element 122 to teeth insert124, which is fastened rigidly to element 122. When engaged due toactuation (axial translation) of element 122, teeth insert 124 mesheswith teeth insert 126 enabling transmission of torques that oppose kneeflexion. Teeth insert 126, rigidly fastened to housing 120, transmitstorques to housing 120 via its fasteners. Finally, housing 120, which isrigidly fastened to outer support ring 128, transmits torque to outersupport ring 128 via fasteners (not shown). In this manner, torques canbe transmitted from support arm 132 of outer support ring 130 to supportarm 134 of the opposite outer support ring 128. Support arms 132 and 134provide a convenient structure to mechanically interface the lockingmechanism to orthotic bracing. One skilled in the art should recognizethat an equal and opposite torque is transmitted to outer support ring128 and support arm 134 in a similar manner.

Referring to FIG. 14, a stop 136, which can be integral to outer supportarm 132, and a complementary stop (not shown), approximately 180° awayfrom stop 136, acts to interface with arm 134 to mechanically limit therange of relative rotation between,outer rings 128 and 130. This featurecan be used to prevent hyperextension.

FIG. 14 depicts how joint 117 is integrated into an orthotic device.Outer support rings 128 and 130 house joint 117. As shown in FIG. 14,joint 117 is comprised of an electromagnetic coil 118, housing 120,actuating portion 122, and teeth inserts 124 and 126. The outer supportrings are constructed of non-magnetic metallic material. Outer supportring 130 has an attached support arm 132 which attaches to a limbportion of a patient. Similarly, outer support ring 128 has a supportarm 134 that attaches to the same limb portion of a patient as supportarm 132, but joint 117 is aligned with the patient's joint which is tobe supported.

While the invention has been described with respect to certain preferredembodiments, as will be appreciated by those skilled in the art, it isto be understood that the invention is capable of numerous changes,modifications and alterations that are within the scope of the appendedclaims.

What is claimed is:
 1. A method for selectively locking and unlocking anorthotic device associated with a leg of a person comprising aselectively lockable orthotic joint having at least one pressure sensor;an electronic circuit associated with said pressure sensor forgenerating a control signal indicative of at least a threshold pressuresensed by said sensor; and the orthotic joint having a locking mechanismwhich can be selectively locked allowing extension and preventingflexion and unlocked allowing extension and flexion in response to thesensed pressure, comprising: sensing pressure exerted by the person'sfoot with the pressure sensor that communicates with the electroniccircuit; and controlling the orthotic joint with the electronic circuitduring walking by the person, the electronic circuit causing theorthotic joint to be in a locked position that prevents flexion andpermits extension when at least a threshold pressure is sensed by thesensor and in an unlocked position when less than the threshold pressureis sensed by the sensor.
 2. The method of claim 1 wherein said lockingstep locks said joint in the flexion direction.
 3. A selectivelylockable orthotic device for association with the leg of a personcomprising: a selectively lockable mechanical orthotic knee joint thatis capable of flexion and extension movement and having a lockingmechanism that includes means for rigidly locking the knee joint toprevent flexion and to permit extension of the knee joint when the kneejoint is in a locked position and which locking mechanism permitsflexion and extension of the knee joint when the knee joint is in anunlocked position; a pressure sensor for sensing a threshold pressureexerted by the person's foot during walking that is indicative of aperson placing at least a portion of his weight on the leg associatedwith the device; and an electronic control circuit for controlling saidmeans for rigidly locking and unlocking of the knee joint during walkingthat causes the knee joint to be in the locked position when at leastthe threshold pressure is placed on the foot of the person and sensed bythe pressure sensor and in the unlocked position when less than thethreshold pressure is placed on the person's foot and sensed by thepressure sensor.
 4. The selectively lockable orthotic device of claim 3wherein said electronic circuit is electrically connected to saidpressure sensor and said orthotic joint.
 5. The selectively lockableorthotic device of claim 3 wherein said mechanical orthotic jointincludes: an energizable electromagnetic coil; a spring washer which isdeflectable in an axial direction when said electromagnetic coil isenergized; a first plate having a face comprised of a plurality ofspaced teeth; and a second plate having a face comprised of a pluralityof spaced teeth which are complementary to said plurality of spacedteeth of said first plate, said second plate being deflectable in anaxial direction such that said plurality of spaced teeth of said secondplate engage said plurality of spaced teeth of said first plate whensaid electromagnetic coil is energized, wherein the engagement of saidfirst and second plates locks movement of said orthotic joint in atleast one direction when said second plate engages said first plate. 6.The selectively lockable orthotic device of claim 5 wherein said secondplate comprises a low hysteresis magnetic material which is deflectedwhen said electromagnetic coil is energized.
 7. The selectively lockableorthotic device of claim 3 wherein when said orthotic joint whenunlocked is moveable in a flexion direction and an extension directionand when said orthotic joint is selectively locked the orthotic joint ismoveable only in the extension direction.
 8. The device of claim 3wherein when the knee joint is unlocked, the electronic control circuitis capable of generating a locking signal that locks the knee joint whenat least the threshold pressure is sensed by the sensor.
 9. The orthoticdevice of claim 3 wherein said means for rigidly locking comprises atleast two plates with intermeshing teeth.
 10. An orthotic devicecomprising: at least one pressure sensor which generates a lockingcontrol signal when at least a threshold pressure level is sensed; atleast one mechanical orthotic joint having a locking mechanism which canbe selectively locked to prevent flexion and to permit extension andunlocked to permit flexion and extension in response to the presence orabsence of the locking signal respectively, said joint furthercomprising an electromagnetic coil that is energized when said controlsignal is received; an electronic circuit operatively connecting saidpressure sensor to said orthotic joint; a spring washer which isdeflectable in an axial direction when said electromagnetic coil isenergized; a first plate having a face comprised of a plurality ofspaced teeth; and a second plate having a face comprised of a pluralityof spaced teeth which are complementary to said plurality of spacedteeth of said first plate, said second plate being deflectable in anaxial direction such that said plurality of spaced teeth of said secondplate engage said plurality of spaced teeth of said first plate whensaid electromagnetic coil is energized, wherein said first and secondplates are immovable with respect to each other thereby preventingmovement of said orthotic joint in the flexion direction and beingmoveable in the extension direction.